body{
	margin: 0;
	padding: 0;
	height: 100%;
	width: 100%;
}
#ul{
	list-style: none;
}
#ul button{
	border: 1px solid  black;
}
#f_class{
	display: block;
}
#f_stu{
	display: none;
}
th{
	text-align: center;
}
#list td{
	line-height: 30px;
}
#b_class,#b_stu{
	margin: 20px;
	float: left;
}
#b_stu{
	display: none;
}
#t_class{
	display: table;
}
#t_stu{
	display: none;
}